Only a limited number of molecules with demonstrated therapeutic value can be transported through the skin via unassisted or passive transdermal drug delivery. The main barrier to transport of molecules through the skin is the stratum corneum (the outermost layer of the skin).
Devices including arrays of relatively small structures, sometimes referred to as microneedles or micro-pins, have been disclosed for use in connection with the delivery of therapeutic agents and other substances through the skin and other surfaces. The devices are typically pressed against the skin in an effort to pierce the stratum corneum. The microneedle arrays are generally used once and then discarded.
Microneedles on these devices pierce the stratum corneum upon contact, making a plurality of microscopic slits that serve as passageways through which molecules of active components (e.g., therapeutic agents, vaccines, and other substances) can be delivered into the body. In delivering an active component, the microneedle array can be provided with a reservoir for temporarily retaining an active component in liquid form prior to delivering the active component through the stratum corneum. In some constructions, the microneedles can be hollow to provide a liquid flow path directly from the reservoir and through the microneedles to enable delivery of the therapeutic substance through the skin. In alternate constructions, active component(s) may be coated and dried on the microneedle array and delivered directly through the skin after the stratum corneum has been punctured.
Transdermal adhesive patches are also available and are generally constructed as an adhesive article with a pressure sensitive adhesive coated onto the surface of a backing comprised of a polymeric film, cloth or the like. Transdermal adhesive patches are provided with an adhesive that allows the patch to be releasably adhered to the surface of the skin where a predetermined dosage of an active component can be put in contact with a small surface area of the skin. An appropriate biocompatible carrier is normally provided to facilitate the absorption of molecules through the stratum corneum over a period of time while the patch remains adhered to the skin.